25 March 2026, Volume 37 Issue 1

    

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DIGITAL INTELLIGENCE APPLICATION
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  Design and deployment of OffshoreGPT, a specialized large language model for offshore oilfield mud logging

  ZHOU Guangyuan, FANG Zhendong, WANG Hongna, JIANG Hui, BAI Linkun

  Mud Logging Engineering. 2026, 37(1): 1-7. https://doi.org/10.3969/j.issn.1672-9803.2026.01.001

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  To enhance the real-time data analysis and intelligence level of offshore oilfield mud logging operations, a large language model OffshoreGPT for mud logging tasks has been constructed. This model was pre-trained based on 7 405 structured domain paragraphs and approximately 6 000 high-quality "question-answer pairs". The Supervised Fine-Tuning and Instruction Tuning strategies are combined to improve the domain term analysis and professional text generation ability. And the full-process training is completed in a high-performance server environment equipped with multiple GPU cards, ensuring stability and fast response capabilities under complex working conditions. The test results show that OffshoreGPT has achieved an increase of 81.77% in BLEU-4 score and 63.43% in ROUGE-L score in domain knowledge questions and answers and fault diagnosis tasks. In the simulated mud logging scenarios, it can real-time identify key operational events and generate risk alerts, thereby improving operational accuracy and safety while reducing manual intervention. The model has shown good adaptability in on-site technical support, indicating that it is both feasible and advantageous for the intelligent application of mud logging operations in offshore oilfields.
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  Research & development and application of intelligent generation system for well completion geological reports

  MA Fugang, CUI Guohong, LUO Peng, YUAN Renguo, ZHANG Heng, LIU Shaofeng

  Mud Logging Engineering. 2026, 37(1): 8-14. https://doi.org/10.3969/j.issn.1672-9803.2026.01.002

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  Well completion geological reports serve as critical deliverables in oil and gas exploration and development. Addressing the inefficiencies, error-prone nature, and lack of standardization inherent in traditional manual compilation methods, this study developed an intelligent generation system based on the GeoWell software. Leveraging data provided by CNOOC's EOM data lake, the system enables batch import and parsing of multi-source data including mud logging, well logging, and testing records. Guided by CNOOC corporate standards and incorporating geologist experience, it constructs a configurable rule repository and structured templates. Employing a closed-loop architecture of "data access→rule-based decision→content assembly→standard output", it integrates data mapping, dynamic content generation, and automated typesetting to achieve one-click conversion from raw data to standardized reports. Scaled application across 158 wells in the Bohai Oilfield demonstrates that this system boosts report preparation efficiency by over 73%, significantly enhances data accuracy and formatting compliance, and effectively facilitates the transition of geologists from transactional tasks to high-value analytical research. It provides a model for the digital and intelligent transformation of oil and gas geological operations.
EQUIPMENT R & D
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  Equipment R&D and application of helium rapid detection while drilling

  PENG Chuan, WANG Zhenhua, LI Jianwei, QI Zhenzhen, CHENG Haohua, ZHANG Zhen

  Mud Logging Engineering. 2026, 37(1): 15-20. https://doi.org/10.3969/j.issn.1672-9803.2026.01.003

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  Helium is a scarce strategic resource indispensable for national defense construction and the development of high-tech industries. Helium-containing natural gas is currently the only source for industrial helium production. The existing helium detection technologies mainly rely on laboratory mass spectrometer detection and on-site chromatography+thermal conductivity detector （TCD） detection. The former has discontinuous detection data, while the latter has problems such as long cycle and insufficient detection accuracy, making it difficult to meet the real-time evaluation needs while drilling exploration. To overcome the technical bottlenecks mentioned above, the equipment for helium rapid detection while drilling was researched and developed. The equipment mainly consists of a mass spectrometry detection system, an anti-interference preprocessing system, and a supporting control software system. Core unit mass spectrometry detection system is composed of an electronic ionization system, a quadrupole mass analyser screening system, and an electronic multiplier detection system, and is equipped with special data processing software. With a rack-mounted portable design, it seamlessly integrates with comprehensive mud logging units. Its minimum detectable limit for helium is 2×10⁻⁶, with an analysis cycle of 30 s. It can realize synchronous analysis, data processing, mapping output and real-time monitoring with comprehensive mud logging units, providing equipment support and technical assurance for rapid helium detection while drilling and reserve estimate. The equipment has been applied to the fields in the Ordos Basin and the lower Yangtze Basin. The detection data show good consistency with the laboratory test results for helium from the natural gas. The application has shown significant effects, providing important technical support for the efficient exploration and development of helium-bearing gas pool.
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  R&D and application of online overflow and lost circulation monitoring system for drilling fluids

  WANG Jun, JIANG Yahui, WANG Hongwei, ZHAO Tianhua, LI Tie, YUAN Boyan

  Mud Logging Engineering. 2026, 37(1): 21-27. https://doi.org/10.3969/j.issn.1672-9803.2026.01.004

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  The outlet flow rate of drilling fluid is one of the key parameters to monitor the downhole overflow and lost circulation in mud logging engineering. Given that conventional target type flowmeters and other measurement methods are affected by non-full pipe flow regimes, on-site vibrations, and medium characteristics, resulting in low measurement accuracy and significant delay in early warning, they are unable to meet the requirements for high-precision safe drilling. A drlling fluid online overflow and lost circulation monitoring system based on radar hydrodynamometer, radar liquidometer, high definition camera, and multiparameter fusion model has been researched and developed, which realizes real-time online measurement of drilling fluid outlet flowrate under non-full pipe conditions. Compared with the comprehensive mud logging units, it can detect overflow and lost circulation anomalies 1 to 3 minutes earlier and give an alarm. The wellsite application indicates that the system is easy to install, simple to operate, and has low maintenance costs, effectively solving the problem of low measurement accuracy of non-full pipe flowrate and providing reliable technical support for drilling safety.
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  Design and application of a multi-channel signal detection system for modular mud logging instruments

  REN Zhonghong, YANG Dan, ZHAO Teng, WANG Jiawei, LIU Bojin, ZHANG Yunxiang

  Mud Logging Engineering. 2026, 37(1): 28-33. https://doi.org/10.3969/j.issn.1672-9803.2026.01.005

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  To meet the development needs of modular mud logging instruments and achieve the intelligence and automation of channel signal detection systems, a multi-channel signal detection system for modular mud logging instruments has been developed. The system utilizes standard signal generation circuits and data acquisition circuits for rapid, accurate and intelligent detection of the channel signals in the instrument acquisition system. The metering results have traceability and transmissibility, meeting the requirements of petroleum industry standards. The application results show that the detection system has high level of intelligence, small errors and powerful functions, realizes the accurate detection of mud logging instrument channel signal, and further improves the quality of wellsite mud logging services.
TECHNOLOGY
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  R&D and application of continuous monitoring technology of downhole liquid level in drilling-mud logging integration

  ZHANG Liang, XIE Ping, WANG Haochen

  Mud Logging Engineering. 2026, 37(1): 34-41. https://doi.org/10.3969/j.issn.1672-9803.2026.01.006

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  When the annulus liquid level is not at the wellhead during the drilling process, in order to solve the technical difficulties of continuousiy monitoring downhole liquid level, the lack of automatic means for identifying the fluid level depth, and the inability to link with drilling engineering parameters to guide the decision-making of the whole overflow and lost circulation process in the well opening state, the drilling-mud logging integration downhole liquid level continuous monitoring technology and its application program are proposed. Based on the actual situation on site, the study is conducted on the sensor-based design of downhole liquid level monitoring instruments and their deep integration with the compound logging. By optimizing the installation location to reduce acoustic interference, the problem of continuous monitoring in the well opening state has been solved. The correlation algorithm based on the periodic attenuation characteristics of echoes solves the problem of downhole liquid level automatic identification and improves the automation extent of continuous monitoring. The technology interacts with the compound logging system for data exchange and monitors real-time curves. Combined with the liquid level depth, the dynamic models of wellbore leakage for calculating leakage rate and the lost circulation volume were established, realizing the application of drilling engineering-compound logging integration in the case of lost returns for lost circulation. The purposes of real-time monitoring, analysis, alarm and recording of downhole conditions and overflow and lost circulation situations are achieved. In practical application cases on well sites, real-time monitoring of well opening has achieved good application results, realizing dynamic warning under lost returns for lost circulation conditions and accurately guiding plugging decisions, and providing strong guarantees for well control safety.
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  A method for complex lithology identification based on digital rock image analysis

  HAO Yang, DU Huanfu, WAN Yaqi, ZENG Xiang, WANG Xin

  Mud Logging Engineering. 2026, 37(1): 42-48. https://doi.org/10.3969/j.issn.1672-9803.2026.01.007

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  With the significant progress in mud logging analysis technology,cuttings mineralogical identification technology represented by RoqSCAN has become an important tool in mud logging analysis. However,this technology currently can only test the mineral composition within cuttings particles and cannot achieve automatic lithology identification,making it even more difficult to identify complex lithologies. Therefore, a complex lithology identification method based on digital rock image analysis was proposed, i.e., using edge detection and image segmentation techniques to achieve the automatic extraction of rock particles, combining particle morphology and mineral information to conduct particle-level lithology identification, and providing scientific and reliable data support for the identification and classification of complex lithologies through statistical and visual analysis of the identification results. At present, this recognition method has been successfully applied to well D 2 in Ordos Basin, significantly improving the accuracy and efficiency of identifying complex strata, and providing a new technical method for efficient identification of the cuttings in mud logging sites.
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  Quantitative calculation method of rock cutting fluorescence content based on image processing techniques

  GUAN Baoluan, XIE Yingming, LI Zhankui, JIN Kun, WANG Jun

  Mud Logging Engineering. 2026, 37(1): 49-56. https://doi.org/10.3969/j.issn.1672-9803.2026.01.008

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  Aiming at the problems of uncertainty and instability of rock cutting fluorescence observed by human eyes in the field exploration and development, research on the method of quantitative calculation of rock cutting fluorescence content based on image processing technology was carried out. After comparing characteristics of Robert, Prewitt, and Sobel operators, Sobel edge detection operator and morphological algorithm are finally selected to accurately lock the rock cutting area, and then the images of the rock cutting area are converted to HSV space to extract specific fluorescence areas, so as to realize the quantitative expression of the fluorescence content of rock cuttings. Meanwhile, through comparing, it can be seen that the error between this method and the manually chosen region is less than 5%, and the error of fluorescence content extraction is less than 0.2%, the correct rate of field application is 98.35%, which indicates that this method has a high degree of accuracy, and it can effectively overcome the problems of uncertainty and insufficient quantification of human eye recognition, enhance the mud logging work efficiency, and have great significance in advancing the intelligent development of the mud logging technology intelligently.
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  Clastic rock granularity evaluation method based on machine learning+element logging： A case study of Xihu Sag, East China Sea Basin

  SONG Yunxuan, YUE Xue, ZHANG Guodong, WANG Lei, LU Fawei

  Mud Logging Engineering. 2026, 37(1): 57-64. https://doi.org/10.3969/j.issn.1672-9803.2026.01.009

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  To address the challenges in deep exploration of Xihu Sag, East China Sea Basin, where PDC bits cause severe damage to original formation particles, making accurate analysis of clastic rock granularity from cuttings difficult, and where drilling coring and sidewall coring are costly and time-consuming, this study establishes a method of rapid and accurate clastic rock lithology granularity evaluation while drilling. Based on element logging data and geological mechanism analysis, typical element combinations related to granularity were optimized. Machine learning methods were then employed to establish predictive models for different series of strata： linear regression for Huagang Formation, and decision tree and random forest algorithms for the upper and middle sections of Pinghu Formation, respectively. This summarizes a clastic rock granularity evaluation method applicable to different series of strata in Xihu Sag. Practical applications demonstrate that this method achieves an overall accuracy rate of 89.7% in predicting lithology granularity in Huagang and Pinghu Formations of Xihu Sag, effectively identifying 7 granularity levels from mudstone to glutenite. It provides reliable technical means and reference basis for sweet spot evaluation while drilling and subsequent operational decisions in clastic rock reservoirs of Huagang and Pinghu Formations in Xihu Sag.
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  Application and progress of fractal theory in characterization of tight reservoir pore structure

  LI Junjun, QI Yuantao, YU Chunyong, BAI Jinhao, XIE Penghui, LIAO Siyi

  Mud Logging Engineering. 2026, 37(1): 65-76. https://doi.org/10.3969/j.issn.1672-9803.2026.01.010

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  With the rapid expansion of oil and gas exploration into deep, ultra-deep, and unconventional domains, reservoir rocks have become increasingly tight. Pore scales have shrunk dramatically from millimeters to micrometers and even nanometers, while pore numbers have increased exponentially and pore-size distributions have broadened substantially. These changes have led to a significant rise in pore-structure complexity. Under such conditions, traditional direct observation and mercury intrusion techniques can no longer adequately characterize nanometer-scale pore structures, nor can they effectively quantify their strong heterogeneity. Gas adsorption （N₂/CO₂） and nuclear magnetic resonance （NMR） techniques enable the detection of micro-and nanopores. When combined with fractal geometry theory, the fractal dimension （D） can quantitatively describe the cross-scale self-similarity of pore structures, offering a new pathway to tackle this challenge. This study systematically reviews mainstream fractal modeling approaches based on mercury injection capillary pressure curves, gas adsorption isotherms, and NMR relaxation spectra; compares their applicability ranges and complementary strategies across nano-to micrometer scales; and summarizes quantitative models linking fractal dimensions with reservoir properties such as permeability and gas content. Results indicate that integrating fractal dimensions derived from multiple experimental techniques can establish a full-scale complexity evaluation system covering micropores, mesopores, and macropores, thus providing theoretical support for sweet-spot prediction in unconventional reservoirs. Looking ahead, AI-driven dynamic fractal correction methods and multi-source data fusion models represent important future directions for pore-structure fractal analysis.
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  Characteristics and gas-bearing property logging evaluation of tight sandstone reservoirs in Jingbian Gas Field

  ZHANG Peng, LIU Yongjian, ZHANG Rui, MA Qi, HE Gang, ZHANG Chao

  Mud Logging Engineering. 2026, 37(1): 77-86. https://doi.org/10.3969/j.issn.1672-9803.2026.01.011

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  The Upper Paleozoic gas reservoir in Jingbian Gas Field is a typical tight sandstone gas reservoir with abundant reserves and resources, and the sandstone geological accumulation conditions of the He 8 Member of Shihezi Formation and Shanxi Formation are superior, which are the main successor layer is for long-term stable production of the gas field. However, the strong reservoir heterogeneity and great difficulty for gas-bearing property evaluation severely restrict the efficient development of gas field. In order to further clarify the reservoir characteristics and development potential of tight sandstone gas reservoirs, based on core observation, thin section identification, physical property testing, logging interpretation and other technologies, combined with gas testing and production data, the fine study on reservoir characteristics and gas-bearing property logging evaluation of He 8 Member are deepened. The gas-bearing property lower limit of the reservoirs was determined through the establishment of well logging crossplot charts, and on the basis of detailed classification and evaluation of the reservoirs, the favorable gas-bearing areas of the reservoirs were evaluated and predicted. The results show that the rock types of He 8 Member are mainly detritus sandstone and detritus quartz sandstone, quartz sandstone is secondary, but the physical properties of quartz sandstone is better than detritus quartz sandstone and detritus sandstone. Secondary porosity such as rock debris dissolution holes, inter-granular dissolution holes, and inter-crystalline holes control the formation of effective reservoir space. The predicted favorable reservoir gas-bearing areas are classes Ⅱ and Ⅲ, which are distributed in the central and eastern parts of the study area. The study results provide a certain geological evidence for development potentials and exploration employments of the Upper Paleozoic gas reservoirs in Jingbian Gas Field.
INTERPRETATION & EVALUATION
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  Analysis of the abnormal causes for the reverse order of gas logging components and fluid intelligent identification model construction for shallow Wushi Sag, South China Sea

  HUANG Kaizhan, CHEN Pei, LIU Wei, ZHONG Peng, XIA Yang, MO Guoyan

  Mud Logging Engineering. 2026, 37(1): 87-92. https://doi.org/10.3969/j.issn.1672-9803.2026.01.012

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  Regarding the reverse order anomaly of the "high heavy hydrocarbon, low light hydrocarbon" gas logging components encountered in Neogene shallow layers of Wushi Sag in the western South China Sea, and the problems it causes in fluid property identification and low reservoir evaluation accuracy, taking Wushi A oilfield as an example and combining with the geological background and the characteristics of the gas logging data, it is clear that the anomalies are mainly distributed in areas such as the slope belt and the inversional structure belt. The formation mechanism of gas logging anomalies in the study area is proposed as "lateral migration fractionation+vertical gravitational differentiation". On this basis, a reservoir fluid intelligent identification model based on random forest algorithm is constructed. The model is characterized by total hydrocarbon and C₁-C₅ components of gas logging, and is trained and optimized by using historical data of 40 wells in the study area. Practical applications have shown that the model achieves an overall coincidence rate of 80.1% in identifying fluids of abnormal intervals for gas logging components with reverse order in 21 wells. The study results provide new theoretical and technical basis support for the precise identification of fluids in shallow low-resistivity reservoirs and similar complex hydrocarbon reservoirs in the western South China Sea, and have important guiding significance for improving the efficiency of oil and gas exploration and development.
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  Geological characteristics and favorable target optimization for 8^# coal seam in Benxi Formation of Su X block in northern Sulige Gas Field

  WANG Hongyuan, LI Yuying, LI Guoliang, FANG Jinwei, DUAN Chuanli, SUN Hao

  Mud Logging Engineering. 2026, 37(1): 93-103. https://doi.org/10.3969/j.issn.1672-9803.2026.01.013

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  To realize the exploration and development of the deep coal-rock gas in Su X block, northern Sulige Gas Field, the research method of "experimental analysis-well logging modeling-planar distribution analysis-favorable target optimization " was adopted, and a systematic evaluation was conducted on the 8^# coal seam in Benxi Formation of this block. Based on laboratory data from key cored wells, through systematic analysis of the characteristics such as the gas concentration, petrology, physical properties, microscopic pore structure and rock mechanics of the coal seams, it has been made clear that the coal seams in this block have the reservoir bases of the poor development of a primary-cataclastic texture, millipore and cleat, ultra-low permeability, medium brittleness, etc. Through the regression analysis of core experimental data and corresponding logging curves, a well logging interpretation model for key parameters such as industrial components, gas concentration, porosity, and permeability applicable to this block was established, achieving accurate and continuous evaluation of coalbed methane reservoirs. On this basis, the target coal seam′s buried depth, thickness, spatial distribution of interbedded gangue layers and the other key geological conditions were comprehensively analyzed, and the evaluation criteria of favorable targets were established from the coupling perspective of multiple factors such as coal seam thickness, planar distribution characteristics, coal-rock ash, coal-rock gas concentration, tectonic setting, roof lithology and the number of interbedded gangue layers. The favorable target areas for coal-rock gas development have been delineated, providing an important basis for the next exploration deployment of deep coal-rock gas in this block.
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  Application of geological engineering comprehensive evaluation method in tight sandstone gas reservoirs of Shenfu Block

  WU Fang, ZHU Haoyu, YANG Fei, LI Xinliang

  Mud Logging Engineering. 2026, 37(1): 104-111. https://doi.org/10.3969/j.issn.1672-9803.2026.01.014

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  The tight sandstone reservoirs in Shenfu Block are characterized by low porosity, low permeability, small pore throats, and strong heterogeneity, leading to significant deviations between actual productivity and predicted values after fracturing in some optimized reservoirs. To address this core issue, a geological sweet spot index（D_G） was constructed based on key parameters such as excavation effect index, permeability, total hydrocarbon content, and reservoir pressure. Combined with brittleness index and reservoir stress difference coefficient, an engineering sweet spot index（F_E） was established, and then coupled to form a reservoir geology-engineering dual sweet spot index（S_I） evaluation model. Analysis reveals that sand stone confining pressure difference is greater than 3.3 MPa, with S_I greater than 0.44, indicating Class I sweet spot area. When S_I is of 0.35-0.44, it is Class Ⅱ sweet spot area. When S_I is less than 0.35, it belongs to Class Ⅲ non-sweet spot area. Application examples verify that this dual sweet spot evaluation model simultaneously considers the differences in confining pressure difference and intrinsic reservoir quality, effectively screening high-quality stimulation targets, providing reliable technical support for the development deployment of tight sandstone reservoirs and the optimization of fracturing sweet spot areas.
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  Identification method of oil and gas shows by 3D quantitative fluorescence logging under the condition of constant rheology FLAT-PRO synthetic-based drilling fluid

  HU Xiaoxiao, LIAO Gaolong, LYU Wenhai, SUN Benfei, ZHANG Guoliang

  Mud Logging Engineering. 2026, 37(1): 112-118. https://doi.org/10.3969/j.issn.1672-9803.2026.01.015

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  In deep-water exploration in Qiongdongnan Basin, the constant rheology FLAT-PRO synthetic-based drilling fluid contains high concentrations of fluorescent additives, which causes traditional 3D quantitative fluorescence（3D-QF） logging to be affected by background interference and fluorescence quenching, making it difficult to accurately identify oil and gas shows.To address this issue, this study focuses on eliminating or mitigating the interference of the constant rheology FLAT-PRO synthetic-based drilling fluid on 3D-QF logging. By analyzing the fluorescence spectral characteristics of synthetic-based drilling fluid additives and designing gradient mixing experiments of crude oil samples with drilling fluid filtrate, the interference mechanism is clarified. A standardized method for subtracting the drilling fluid background spectrum is established, which enables effective identification of reservoir oil-bearing characteristics and quantitative evaluation. Field applications in wells LX 30-1 and LX 30-2 have verified that this method can rapidly and accurately identify oil and gas shows, significantly improving the detection accuracy and reliability of 3D-QF logging under synthetic-based drilling fluid conditions. This research provides effective technical support for oil and gas exploration in complex formations.
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  Evaluation methodology for low-porosity and low-permeability reservoirs based on LWD density and FLAIR fluid logging： A case study of south Kaiping Oilfield, Pearl River Mouth Basin

  DING Fengjuan, XIONG Ting, CAO Yingquan, DENG Zhuofeng, ZHU Jingwen

  Mud Logging Engineering. 2026, 37(1): 119-124. https://doi.org/10.3969/j.issn.1672-9803.2026.01.016

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  To solve the reservoir effectiveness identification problems in south Kaiping Oilfield, Pearl River Mouth Basin,based on the characteristics of well logging and mud logging technologies, the methodology for rapid evaluation while drilling with regional characteristics and well logging and mud logging combination for low-porosity and low-permeability reservoirs was developed. The specific methods are as follows. （1） Establish a reservoir effectiveness index（I_D） to rapidly evaluate reservoir effectiveness by statistically analyzing mobility data of formation pressure measurement. （2）Correct the FLAIR gas logging data to obtain corrected methane content per unit volume of rock（VC1）, and use the normalized abnormal multiple value （AC1） to construct the reservoir oil saturation index（X）. （3）Based on regional pressure measurement sampling and testing data calibration, a chart and criteria for well logging and mud logging combined interpretation and evaluation were constructed by using I_D and X, realizing rapid evaluation of low-porosity and low-permeability reservoirs. The application results at the well site show that the methodology has a coincidence rate of over 85% in rapid interpretation while drilling in south Kaiping Oilfield, effectively guiding the subsequent formulation of cable pressure measurement sampling plans and operating decisions. It has achieved considerable economic benefits and has broad prospects for promotion and application, exploring a new way for rapid evaluation of the complex reservoirs.
GEOLOGICAL RESEARCH
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  Genesis analysis of rhyolite "knife-cut-like" texture and its significance for reservoir evaluation

  LI Wenyuan, LI Zhankui, LUO Peng, MA Jinxin, YUAN Renguo, LI Panpan

  Mud Logging Engineering. 2026, 37(1): 125-130. https://doi.org/10.3969/j.issn.1672-9803.2026.01.017

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  To explain the genesis of the "knife-cut-like" texture in rhyolite from Sheshan, Shanghai, and to explore its enlightenment significance to the formation mechanism and evaluation methods of rhyolite reservoirs, through field observation, thin section analysis, and Bohai downhole data analysis, the development stages（fracture formation period, I-shaped period, V-shaped period and W-shaped period） were divided, and the microscopic pore structure and dissolution characteristics of the rhyolite were also analyzed in depth. The results indicate that the rhyolite "knife-cut-like" texture is a product of preferential dissolution of fractures under prolonged freshwater leaching, demonstrating rhyolite′s high inherent dissolubility, and fractures critically facilitate secondary dissolved pore formation, both of which constitute the core mechanism of reservoir formation. Based on this, a reservoir evaluation method combining element logging（K element characterizing dissolution factor, Si element characterizing devitrification factor） and a standardized mechanical specific energy model（fracture factor） was proposed. The comprehensive evaluation models for different zoning（weathering crust/parent rock zone） were established using the Analytic Hierarchy Process（AHP）, achieving a 91% coincidence rate with well logging interpretation in well X application within Bohai Sea, and providing pivotal evidence and theoretical support for the coupling mechanism of dissolution-fracture in volcanic rock reservoirs.
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  Fault segmentation and evolution of the Fengxi structure of western Qaidam Depression and its control on multi-type traps and reservoirs

  HE Li′an, FENG Ning, CAO Fei, FU Jiyou, CHEN Yao, CAO An′an

  Mud Logging Engineering. 2026, 37(1): 131-137. https://doi.org/10.3969/j.issn.1672-9803.2026.01.018

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  The Fengxi structure in the western Qaidam Depression is a significant hydrocarbon exploration target in the western Qaidam Basin. However, previous studies have suffered from insufficient understanding of key geological features such as fault architecture and activity stages. Based on detailed interpretation of 3D seismic data and integrated application of seismic attribute analysis techniques, this study systematically clarifies the segmented architecture of the Fengnan and Fengbei fault zones and reconstructs the tectonic evolution sequence, ultimately forming a fault-controlled anticlinal configuration characterized by "two faults sandwiching a uplift." Multi-phase tectonic activities not only governed the evolution of structural morphology but also played a dominant role in the development of diverse trap types. Based on the updated fault model, three trap types are identified: faulted anticlines, multi-layer traps in the lower wall brim, and fault-bounded blocks. A composite trap accumulation model is established, and the reservoir-forming mechanisms of three reservoir types （Type A： structural-lithologic controlled; Type B： fault-lithologic controlled; Type C： fault controlled） are clarified. Differentiated well location deployment strategies are proposed. Horizontal wells deployed for Type A reservoirs have achieved positive production results as verified by drilling. This study deepens the understanding of the "fault-trap-reservoir" system in the Fengxi structure and establishes a collaborative analysis framework integrating "fault segmentation-trap types-reservoir mechanisms", providing a reliable geological basis for oil and gas exploration and development.
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  Main control factor analysis of reservoir development in the second Member of Bayingebi Formation,eastern slope of Tiancao Sag

  ZHANG Hua, JING Wenbo, TANG Xinping, WANG Yu, WANG Gang, XU Xiongfei

  Mud Logging Engineering. 2026, 37(1): 138-144. https://doi.org/10.3969/j.issn.1672-9803.2026.01.019

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  The eastern slope of Tiancao Sag is rich in oil and gas resources in the second Member of Cretaceous Bayingebi Formation,but faces challenges including rapid reservoir lateral changes and unclear developmental control factors,which constrain the hydrocarbon reservoir exploration progress in this area. Therefore,adopting a structure-sedimentation coupling research approach and integrating technical methods such as seismic interpretation,paleogeomorphology restoration,core observation,thin section identification,and log facies analysis,this study systematically investigated the structural characteristics,sedimentary reservoir distribution patterns,and their coupling relationships on the eastern slope. The results are obtained in three aspects. （1）The eastern slope of Tiancao Sag develops major long-term active faults that control sedimentation,which continuously move with tectonic activities, forming fault slope-break belts. These fault slope-break belts significantly control sedimentation,resulting in steeper topography near the slope-break belts and abrupt changes in stratum thickness on both sides of the slope-break. （2）During the sedimentary period of the second Member of Bayingebi Formation,the main sedimentary facies on the eastern slope was braided river delta front,which can be further divided into two facies belts of inner-front and outer-front. The delta inner-front facies belts is closer to the provenance,with faster sedimentation rate,poorer rock sorting,and inferior porosity-permeability conditions. The delta outer-front facies belt is relatively farther from the provenance,where sediments are more strongly modified by lake water,with better sandstone sorting,favorable for pore development and connectivity,and better porosity-permeability conditions. （3）Overlay analysis of fault slope-break belts and sedimentary facies shows significant differences in sedimentary microfacies on both sides of the fault slope-break belts. The fault slope-break belts precisely serve as the boundary between inner and outer fronts. Above the fault slope-break belts,the delta inner-front facies belt mainly develops,with sedimentary microfacies primarily being underwater distributary channels, characterized by coarser lithology,poorer sorting,and inferior physical properties. Below the fault slope-break belts,the delta outer-front facies belt mainly develops,with sedimentary microfacies primarily being underwater distributary channels and mouth bars,characterized by finer lithology,better sorting,and better physical properties,making it a favorable reservoir development area. The research findings provide theoretical basis and practical reference for hydrocarbon reservoir exploration in Tiancao Sag and similar geological conditions areas.
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  Waterflooding rule and remaining oil enrichment modes in high water-cut stage of Bohai L oilfield

  ZHANG Xiumin, CHEN Shoucun, ZHANG Yafei, WANG Liya, GUAN Jinging

  Mud Logging Engineering. 2026, 37(1): 145-152. https://doi.org/10.3969/j.issn.1672-9803.2026.01.020

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  Bohai L oilfield has entered the high water-cut development stage,where prominent issues of uneven vertical and areal reservoir utilization have led to highly dispersed remaining oil distribution,limiting the effectiveness of conventional measures of tapping potential. To enhance oil recovery,based on detailed geological research,the main control factors of the waterflooding rule were systematically analyzed through integrated approaches including sedimentary microfacies study,restraining barrier and interlayer distribution identification,well logging fine interpretation,and production performance analysis. The study indicates that vertical waterflooding is collaboratively controlled by reservoir rhythmicity,gravity differentiation effect,and restraining barrier and interlayer development characteristics,with the waterflooding location in inverted layered reservoirs determined by the coupling relationship between permeability contrast and gravity effect,where the critical permeability contrast is about 5. The areal waterflooding is mainly controlled by reservoir connectivity dominated by sedimentary microfacies and architecture,fault barrier effects and degree of injection-production well pattern perfection. Based on this,five remaining oil enrichment modes suitable for this oilfield were established, i.e., sand body edge enrichment type,fault barrier enrichment type,contact facies change enrichment type,interlayer-free cut-and-stack facies change enrichment type,and interlayer contact facies change enrichment type. For different enrichment modes,differentiated strategies of tapping potential were proposed,such as using horizontal wells to drill the remaining oil enrichment zones at the top of thick layers or the lower part of the interlayers with precise targets. The results can provide direct technical support for infill adjustment and liquid-producing structure optimization in L olfield,while also offer important references for efficient development of similar high water-cut heavy oil fields.
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  Hydrocarbon accumulation pattern and favorable replacement area distribution for He 6 Member of the Upper Paleozoic non-major reservoirs in Su XX block

  CHEN Wenping, YANG Mingliang, FENG Sen, LI Yuying, SHI Yan, WANG Hongyuan

  Mud Logging Engineering. 2026, 37(1): 153-160. https://doi.org/10.3969/j.issn.1672-9803.2026.01.021

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  A commercial gas flow was obtained from separate testing of the non‑main layer He‑6 Member of the Upper Paleozoic in Su XX block, demonstrating its development potential. To clarify the reservoir‑forming characteristics and guide exploration planning, this study systematically investigates the reservoir characteristics and gas accumulation patterns of the He 6 Member based on well logging, seismic and production data. The research shows that The physical properties of the lower He 6 sub‑member in the study area are comparable to those of the main producing layers, with an average porosity of 5.73% and an average permeability of 0.24 mD, providing a foundation for large‑scale accumulation. Widespread coal‑measure source rocks in the region supply abundant gas. The enrichment pattern can be summarized as "reservoir controlling accumulation, faults controlling enrichment". The differential enrichment of gas reservoirs is mainly co‑controlled by three factors： "reservoir, structure and fault". The distribution of high‑quality reservoirs controls the extent and scale of gas pool, micro‑structural highs control the locations of gas accumulation, and the small‑scale fault systems developed since the Hercynian period serves as key migration pathways, controlling the charging efficiency and enrichment degree of natural gas. Based on the above understanding, combined with reservoir prediction, structural interpretation and fault analysis, three favorable zones have been identified within the block, providing an important basis for production replacement and further deployment in the study area.